Furnace regulation



2 Sheets-Sheet Inventor: Arthur- R Sm ith by iS Attorrw ey.

A. R. SMITH FURNACE REGULATION Filed Jan. 20. 1926 Nov. 19, 1929.

Nov. 19, 1929. A. R. SMITH FURNACE REGULATION Filed Jan. 20, 1926 2 Sheets-Sheet .NMC

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Patented Nov. 19, 1929 UNITED STATES PATENT OFFICE ARTHUR R. SMITH, OF SCHENECTADY, NEW YORK, ASSIGNOR, BY MESNE ASSIGN- MENTS, TO BAILEY METER COMPANY, A CORPORATION OF DELAWARE FURNACE REGULATION "Application and January'ao, 192s. serial No. 82,625.

and Fig. 2 is a similar View of a modification.

Referring' to the drawing, Fig. 1, 1 indicatesa furnace u sed to generate steam in a boiler 2. Powdered fuel is supplied to the furnace by a fuel feeder 3 of any suitable character. The fuel feeder is operated by an electric motor 4, the arrangement .being such that when the speed ofthe motor increases the amount' of fuel supplied to the y furnace increases and when the speed of the motor decreases, the amount of fuel supplied to the furnace decreases.

Electric motor 4 is connected to supply lines 5/and 6 by conductors 7 and 8. 9 indicates the field of the motor and in series with it is a regulating resistance 10 adapted to be cut into and out of circuit by a. contact arm 11 which is moved by a reversing electric motor 12. By operating` motor 12 in one direction or the other, the amount of powdered fuel fed to the furnace can be increased or defreased. y

13 indicates a conduit through which the gases, i. e., products of combustion, from tbe furnace are discharged, and 14 indicates a suction blower for increasing and decreasing tbe draft on the furnace. Suction blower 14 is driven by an electric motor 15 which is conne ted to supply 4lines 5 and 6- by conductors 16 vand 17. When the speed-of motor 15 is increased the draft on the furnace is increased and when the 4speed is decreased the draft is decreased. Suction blower 14 is to be taken as typical of any suitable means for regulating the quantity of air supplied to the furnace.

18 indicates the field of motor 15 andarranged in series with the field is aregulating resistance 19 adapted to lbe cut into and out of circuit by a contact arm 20 whichis moved by a reversing electric motor 21. When motor 21 is operated in one direction it serves tol increase the speed of motor 15 and hence the quantity of air supplied to the furnace, while when it is operated in the other direction it serves to decrease the speed of motor 15 and hence decreases thequantity of air supplied to the furnace.

22 indicates the steam drum of furnace 1. It is connected by a discharge conduit 23 to a header 24. The furnace 1 is one furnace of a number, all of which supply steam to common header 24.

25 indicates dampers for supplyin secondary air to the furnace. They are a apted to be opened and closed by means of an electric motor 26.

27 is an electric flow meter for measuring the amount of air flowing through the furnace. It may be of any suitable type. In the present instance, I have indicated an elec-l tric flow meter of the type'disclosed in the patent to Louis W. Thompson, No. 1,699,126,

-dated January 15, 1929'. It com rises a casing 28 which Vcontains a Inova le element which may be in the form of an inverted bell 29, the lower edge of the bell being sealed in a liquid contained in an annular chamber 30. The opposite sides of bell 29 are connected by trailing and leading pressure pipes 31 and 32 to discharge conduit 13 and to the rst pass in the furnace, respectively. Bell 29 is pivotally connected to a lever 33 which at one end is pivoted on a fixed post`133. ,The other end of lever 33 is connected by a link 134 to an armature 135 upon which is a closed winding 136. In o erative relation to armature 135 is a fiel structure comprising' a winding 137 which is connected to lead wires 34 and 35. The flow meter mechanism illustrated serves to effect oscillating movement of armature 135 in response to changes in the rate of flow of gas through the boiler, and such oscillatin movement varies the current in the circuit of field winding 137 an amount proportional to the movement, providing thereby a measure of the air passing through the furnace.

Conductor 34 is connected to supply line 6. Conductor 35 is connected by a conductor 36 to one coil 37 of a balanced relay 38,-

the other end of the coil being connected by a conductor -39 to vsupply line 5. 'There thus flows through coil 37 of balanced relay 38 a current proportional tothe amount of air flowing throughthe. furnace. 40'is an electric flow -meter of.. any suitable type, it be# ing indicated in the present instance as being of the type described in the patent to Thompson & McNairy, No. 1,560,951iled Nov. 10, 1925. The leading and trailing legs of flow meter 40 are connected by pipes 41 and 42 to a pressure difference creating device 43 inisteam pipe 23. The electric flow meter 40 thus produces'a flow of currentproportionate to the rate of flow of vapor from boiler 1. This is used asa mea'sure of the rateof flow of powdered fuel to the furnace.' it being known that lthere is a definite' relationpbetween the fuel supplied to a furnace and the vapor generated, The circuit of electric. flow meter 40 comprises the conductor 44 Vwhich is connected to' supply line 6 and acondu'ctor 45 which is connected by a c'onductor'46 to one terminal of a coil 47 of relay 38. :The other terminal of coil 47 is connected by a conductor 48 and conductor 39 to supply line5. 'It will thus be -seen that the current flowin in coil 47 is one proportional to the rate 0I flow of vapor from boiler 1 and hence one proportional .to .th'e'amount of fuel being s uppliedto-boiler 1. Coils 37 and 47 of relay 38 are oppositely wound and when the desired 4relation of the currents flowing through'them obtains, the. movable contact 49 of the balanced relay stands midway between two stationary. contacts 50 and '51.' In 'the circuits of coils 37. and 47, are

adjustable resistances 146 and 147 by means of which the relative relation between the currents in the coilsmay-be adjusted which means that the ratio between air'and fuel is adjusted or changed.

Contact 50 is -connected'by aconductor 52 toronel terminal ofthe coil'53 of a magnetic circuit closer, the other terminal being connected 'by a conductor 54 to supply line 6. The contact 51 is connected by'a conductor -to one terminal of a coil 56 of a magnetic circuit closer, the other terminal of which is connected by a conductor 57 to sup ly line 6.- Movable contact 49 is connected y a conductor 58 and conductor 39 to supply line 5,

Connected to header 24 is an electric pressure gauge 59 of any suitable type. In the present instance, it is indicated as being the same general type of instrument as is the flow meter 40, it being understood that as a pres-v sure gauge it measures a differential pressure, this being the dil'erence'in pressure between atmosphere and that in header24. To this end theleading pressure pipe 60 is connected to header 24 and the trailing pressure pipe 61 is open to atmosphere. In this instrument the leading leg of the U-tube is indicated at 62 and the trailing leg at 63, the trailing leg being'long on account of the comparatlvely high pressure to be measured.` It will be understood that the pressure in header 24 maintains the head of mercury in leg 63 and that as the pressure in the headerincreasesl and decreases the mercury rises and fallsl in the trailing leg.

There is thus produced a flow of current in the circuit of pressure gauge 59 which is lproportional to the pressure in header 24.

This circuit comprisesconductor 64 whichis connected to supply line 6, transformer 65, and conductor 66 which connects to one terminal of a. coil 67v which terms a part of a mast-er relay 68, the other terminal of coil 67 being connected by aconductor 69 tothe supply line 5. There is thus produced al flow `of current in coil 67 which .isa measure of the pressure in header 24. The electricv pressure gauge indicated is shown only.A by way of example. Any suitableinstrumentcapable ofvproducing a flow of-current -proportional to pressu're may be utilized.

Master relay 68 comprises a movable contact 70 adapted to engage either of two sta` tionary contacts 71 or 72. Movable contact 70 is connected by a conductor 73 and conductor v39 to.supply li ne 5. Stationary con# tact 71 is -connected by a'condu'ctor 74 to one terminal of the coil 75 of amagnetic circuit closer, .the other terminal being connected by conductor 54 to'supply line'6. Stationary Contact 72 is connected bva conductor 76 to one terminal of,a coil 77ofv a magnetic circuit.

closer, the other terminal of which iscon'-A nected by conductor 57 to'supply line 6.

The control magnet ofwhic-h coil 56 forms a. part when energized, operates a circuit 4close'r 78 which controls-the circuit of -field winding 79 of motor 12` and the control 'magnet of which coil 77 forms 'a part, operates a circuit closer '80 which controls the circuit Y the field windings 83 and 85 of motor 21 serve one to operate the motor in one direction and the other to operate it in the other direction. One terminal of motor 12 is connected to supply line 5 by a conductor 86 and one terminal of motor 21 is connected to supply line 5 by a conductor 87.

88 is an electric pressure gauge of suitable type, it being shown as being an instrument of the same general type as the flow meter 27. It comprises a casing having an inverted bell in it` the trailing side of the bell being connected by a pipe 89 to the first pass of the furnace and the leading side of the bell being connected by pipe 90 to atmosphere. This instrument serves to effect a flow of current in its circuit which is a measure of the pressure in the furnace. The circuit of instrument 88 is connected to a relay 190 which controls the damper actuating motor 2G, by conductor 91, field winding 92, conductor 93, relay 190, and conductor 94 to supply line 6.

The master relay 68 is common to all the furnaces of the system. In connection with each of the furnaces, however, is apparatus the duplicate of that shown and described in connection with furnace 1. 95 indicates the balanced relay for what may be termed furnace No. 2, a'nd 96 indicates the conductors connecting the control magnets for furnace No. 2 to master relay 68. It will be understood that there are as many equipments connected to master relay 68 as there are furnaces to be controlled.

The operation is as follows:

Assume that the various furnaces are burning and that each is supplying vapor through its discharge conduit 23 to header 24. Assume also that the desired pressure exists in header 24. Under these circumstances, the current flowing through the coil 67 of master relay 68 will be such as to maintain movable contact 7() between stationary contacts 71 and 72. Under these conditions, the various parts will be in the positions indicated in the drawing. Motor 4 of each furnace will be running to supply the required amount of fuel to its furnace and the motor of each furnace will be'running to effect the desired supply of air to its furnace.

Assuming also that the desired ratio of fuel to air exists in the case of each furnace, then the flow of current through coils 37 and 47 of each balanced relay 38 will be such as to maintain movable contact 49 midway between stationary contacts 50 and 51.

lf now the pressure in header 24 increases, indicating a decrease in the demand for vapor, then pressure gauge 59 will be operated to efl'eet an increase in the amount of current flowing through Coil G7 of master relay G8. This will cause movable contact 7() to engage stationary contact 72, completing a circuit through coil 77 of the control magnets for motor 12 as follows:

Supply line 5, conductor 39, conductor 73, Contact 70, contact 72, conductor 76, coil 77 and conductor 57 to supply line 6. As soon as this circuit is completed, coil 77 operates to close circuit closer 80 thus completing a circuit through the field winding 8l of motor 12 as follows: Supply line 5. conductor 8G, field winding 81, switch 89 and conductor 57 to supply line G. This operates motor 12 in a direction to decrease the amount of resistance in the field circuit of motor 4. thereby decreasing the speed of motor 4 and hence decreasing the amount of fuel supplied to the furnace. As soon as the supply of fuel to furnace 1 is decreased, the amount of vapor generated in the furnace is decreased and this effects a change in the current in the circuit of flow meter that is the amount of current flowing through balanced relay coil 47. As a result, this relay becomes unbalanced and movable contact 49 engages stationary contact 50. This serves to close the circuit of coil 53 of the control magnets for motor 21 as follows: supply line 5, conductor 39, conductor 58, contact 49, contact 50, conductor 52, coil 53 and conductor 54 to supply line 6. When the coil is energized it effects the closing of circuit closer 82 therebyY closing the circuit of motor 21 through its field winding 83 as follows: supply line 5, conductor 87, field winding 83, circuit closer 82 and conductor 54 to supply line 6. Motor 21 thereupon operates in a direction to increase the amount of resistance in series with the field of motor 15, thereby decreasing the speed of the motor and of suction blower 14. As soon as this occurs, the amount of air passing through the furnace decreases which means that the current flowing in the circuit of flow meter 27 and the coil 37 of balanced relay 38 decreases. As soon as the currents flowing in coils 47 and 37 of balanced relay 38 again reach the desired relation to each other, indicating that the desired relation again exists between the amount of fuel and air supplied to the furnace, then the relay becomes balanced and Contact 49 moves away from contact to its neutral position.

The operation which has been described as taking place in connection with furnace No. 1 takes place also in connection with the other furnaces connected into the system, .so that the amount of vapor generated by each of the furnaces is decreased a proportionate amount.

If now the pressure in header 24 decreases indicating an increase in the demand for vapor, then contact of master relay 68 engages contact 71, thereby closing a circuit through coil of the control magnets for motor 21. This circuit ma be traced as follows: supply line 5, conductor 39, conductor 73, contact 70, contact 71, conductor 74, coil 75 and conductor 54 to supply line 6. This effects the closing of circuit closer y84 thereby closing the circuit of motor 21 through its field winding 85. This causes motor 21 to operate in a direction to increase the amount of resistance in series with the field of motor 15 thereby increasing the speed of motor 15 and hence the amount of air supplied to the furnace. When the amount of air supplied to the furnace increases this is reflected in fiow meter 27, and due to the change in the flow of current through the flow meter circuit which includes coil 37 of balanced relay 38, the relay becomes unbalanced and its movable contact 49 moves into engagement with contact 51. This closes a circuit through coil 56 of the control magnets for motor 12 as follows: supply line 5, conductor 39, conductor 58, contact 49, Contact 51, conductor 55, coil 56 and conductor 57, to supply line 6. lhen coil 56 is energized it actuates circuit closer 78 thus closing a circuit on the field winding 79 of motor 12 as follows: supply line 6, conductor 57, switch 78. field winding 79, and conductor 86, to supply line 5. Motor 12, thereupon operates in a direction to increase the amount of resistance in series with the field 9 of motor 4, thereby effecting an increase in the speed of motor 4 and in the amount of fuel supplied to the furnace. As soon as the amount of fuel supplied to the furnace increases, the amount of vapor flowing from the boiler increases. This increases the amount of electric current flow in the circuit of flow meter 40 thereby increasing the current flowing in balanced relay coil 47. As soon as coils 47 and 37 again become balanced, contact 49 moves from engagement with contact 51 thereby opening the circuit on motor 12. This means that the fuel and air supplied to the furnace again bear the desired relation to each other.

It will be understood that the same operation takes place in each of the other furnaces connected with the system.

In connection with the arrangement, it will be seen that upon a decrease in the demand for steam the amount of fuel to the furnace is first decreased after which the amount of air is decreased to again establish the desired ratio between fuel and air. On the other hand, when the demand for steam increases the supply of air is first increased after which the supply of fuel is increased to again establish the desired ratio between fuel and air. This is a desirable result and b my improved construction is accomplishedy in a simple and satisfactory manner.

By adjusting the resistances 146 and 147, the desired relative relation between fuel and air for all loads in the boiler, may be obtained.

The damper control meter 88 responds to the pressure within furnace 1 and functions through motor 26 to increase and decrease the opening of dampers 25. The arrangement whereby motor 26 operates the dampers 25 is shown only diagrammatically. Any suitable motor operated damper arrangement may be used, the essential thing being that when the fiow of current increases indicating an increase in pressure in the furnace, the dampers will be moved toward closed position while when the pressure in the furnace decreases, the dampers will be moved toward open position. The purpose of the arrangement is to maintain the desired pressure in the furnace for varying operating conditions. lVhen the desired pressure exists in the furnace, relay 190 maintains the contact arm in neutral position as is shown in the drawing. Upon increase or decerase in the pressure in the furnace, relay 190 operates due to the 'change of current flowing in its circuit to close a circuit on motor 26 to effect operation of the motor in a direction to move dampers 25 toward closed or open position as is required to restore the desired pressure in the furnace.

In Fig. 2, I have shown an embodiment of my invention wherein the furnace is supplied with fuel by means of a motor-driven Stoker. The general arrangement and method of operation of the system shown in Fig. 2 1s the same as that shown in Fig. 1, and the same reference numerals. with the exponent a added have been used to designate corresponding parts.

Furnace 1 is supplied with fuel by a mechanical stoker 3'i of any suitable type, driven by an eletric motor 4a. The fuel supply to the furnace is measured by an electrical coal meter 40a which corresponds in function to the flow meter 40 of Fig. 1. That is to say, it effects a flow of electric current in its circuit which is a measure of the amount of fuel supplied to the furnace. Any suitable type of electrical meter adapted for the purpose may be used.

In the present instance, the leading leg of the meter is connected by leading pressure pipe 41a to a device which produces a pressure proportional to the speed at which the Stoker is driven. For this purpose I may employ a suitable tachometer, for example,

a tachometer such as that shown in the patent to R. E. lVoolley, 1,650,679. dated November 29, 1927, the tachometer being driven at a speed proportional to the speed at which the Stoker is driven. The trailing pressure pipe 42 is connected to`atmosphere.

Air is supplied to furnace 1a through a conduit 25 and the quantity of air flowing through conduit 25l is measured by a flow meter 27* which corresponds in function to the flow meter 27 of Fig. 1. In the present instance leading and trailing pipes 30a and 31a measure the drop in pressure across a coil C which is utilized for heating the air passing through conduit 25. Any'suitable medium such as steam, for example, may be used in coil C for effecting the heating. This forms a pressure difference creating device in that the drop in pressure across the coil bears a definite relation to the rate of ow of air through the conduit. In the arrangement shown in Fig. 2 the dampers 25 and the damper-operated motor 26 are omitted as they are not necessary in connection with a stoker fed furnace.

The operation of the arrangement shown in Fig. 2 is similar to that of the arrangement of Fig. 1, differing from it only in that in this arrangement, the master relay 68a, in case of either an increase or decrease in the vapor pressures, acts first on the fuel supply, the relay 38 being then unbalanced and caused to effect a change in the air supplied to bring itwto the desired value for the changed fuel supply.

When the pressure in header 24 is increased, the increased fiow of current through winding 67 of relay 682L causes contact 70 to engage contact 71a. This closes a circuit on coil 56a of the control magnet for the furnace and effects the closing of circuit closer 7 8a. The 'closing of circuit closer 78a closes the circuit on the field Winding 79al of motor 12 which then operates in a direction to decrease the speed of Stoker motor 4, thereby decreasing the amount of fuel fed to the furnace. lVhen the amount of fuel fed to the furnace decreases, this is reflected in coal meter 40a, the decrease in the amount of current fiowing in the circuit of the coal meter causing an unbalance of relay 38". This relay then operates to close a circuit on motor 21a to effect a decrease in the speed of motor 15 and hence a decrease in the amount of air to the furnace. This continues until the amount of air decreases to a value such that the windings 37a and 47a again balance each other. Upon a decrease of the pressure in header 24a the amount of current fiowing in the circuit of pressure meter 59 decreases, whereupon master relay 68a engages contact 72. This closes a circuit on coil 77a of the control magnets, thereby effecting a closing of the circuit closer 80a. This closes a circuit on field winding 81L1 of motor 12a, and motor 12a thereupon operates in a direction to effect an increase in the speed of the Stoker motor 4a, thereby increasing the amount of fuel supplied to the furnace. This again unbalances relay 38El andeffects a clos ing of a circuit on motor 2la in a direction to increase the speed of motor 15, thereby increasing the supply of air to the furnace. When the supply of air reaches the desired value, relay windings 37 and 47HL will again balance each other effecting opening of thc circuit previously closed.

In connection with the description of thc operation of Fig. 2, the circuits have not been traced in detail since they are believed to be obvious from an inspection of the drawing when taken in connection with the decription given in explaining the operation of In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention, together Wlth `the apparatus which I 'now believe to be represented as the best embodiment of my invention, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means.

What I claim as' new and desire to secure by Letters Patent of the United States 1s:

1. In a furnace control system, the combination of means for supplying fuel to the furnace, means for supplying air to the furnace, means which produces a fiow of current which is a measure of the steam flow, means which produces a flow of current which is a measure of the air supplied to the furnace, a balanced relay connected to said two last referred to means, and means responsive to chan es in demand on the furnace for effecting adjustment ofthe fuel and air in accordance with the load, said fuel and air being adjusted relatively to each other through the intermediary of said balanced relay.

2. In a furnace control system, the combination of means for supplying fuel to the furnace, means for supplying air to the furnace, means which produces a flow of current which is a measure of the steam flow, means which produces a flow of current which is a measure of the air supplied to the furnace, a balanced relay connected to said two last named means, and means responsive to changes in demand on the furnace for increasing the amount of air supplied to the' furnace upon increase in load and for decreasing the amount of fuel supplied to the furnace upon decrease in load, said fuel and air being adjusted relatively to each other through the intermediary of said balanced relay.

In a furnace cont-rol system for a plurality of furnaces, the combination of means for supplying fuel to each furnace, means for supplying air to each furnace, means associated with each furnace for effecting a flow of electric current proportional t0 the flow of steam therefrom and to the flow of air thereto, a balanced relay connected to said last named means, and means responsive to changes in demand on the furnaces for effecting adjustment of the fuel and air in accordance with the load, the fuel and air for each furnace being adjusted relatively to each other through the intermediary of said balanced relays.

4. In a furnace control system for a pluralit \v of furnaces, the combination of means for supplying fuel to each furnace, means for supplying air to each furnace, means associated with each furnace for effecting a flow of electric current proportional to the flow of steam therefrom and to the flow of air thereto, a balanced relay connected to said last named means, and means responsive to changes in demand on the furnaces for increasing the amount of air supplied to each furnace upon increase in load and for decreasing the amount of fuel supplied to each furname upon decrease in load, the fuel and air for each furnace being adj usted relatively to each other through the intermediary of said balanced relays.

5. In a furnace control system for a plurality of furnaces, the combination of means for supplying fuel to each furnace, means for supplying air to each furnace, means associated with each furnace for effecting a flow of electric current proportional to the flow of steam therefrom and to the flow of air thereto, a balanced relay connected to said last named means, a measuring device which produces a flow of electric current which changes upon a change in the demand on the furnaces, a master relay connected to said measuring device, and means controlled by said master relay for effecting regulation of the fuel and air to all the furnaces, the fuel and air to each furnace bein adjusted relatively to each other by said alanced relays.

6. The combination with a furnace having means for regulating the amount of air and fuel `supplied to it, of a measuring device for effecting a flow of electric current proportional to the air supply, a measuring device for effecting a flow of electric current proportional to the steam How, a balanced relay connected to said measuring devices, a device responsive to changes in demand on said furnace, and means controlled by said last-named device for effectin adjustment of the fuel and air in accor ance with the demand on the furnace, the air and fuel being adjusted relatively to each other by said balanced relay.

7. The combination with a furnace having means for supplying fuel and means for supplying air thereto, of a control system comprising means which produces a flow of electric current which is a measure of the steam ow, means which produces a flow of electric current which is a measure of the air supplied to the furnace, a balanced relay connected to said two last named means, and means controlled by said balanced relay for adjusting the fuel and air relatively to each other.

8. The combination with a furnace having means for supplying fuel and means for supplying air thereto, of a control system comprising means which produces a flow of electric current which is a measure of the steam How, means which produces a flow of electric current which is a measure of the air supplied to the furnace, a balanced relay connected to said two last named means, means controlled by said balanced relay for adjusting the fuel and air relatively to each other, and adjustable means in the relay connections for changing the relative ratio of fuel and air.

-9. The combination with a furnace having automatic means for varying the amount of fuel and air supplied to the furnace in accordance with the demand 0n the furnace, of means for maintaining the desired relation between fuel and air for all loads comprising, an electric circuit having means therein which effects a flow of current which is a measure of the air iiow, an electric circuit having means therein which effects a flow of current which is a measure of the steam flow, a balanced relay in said circuits, and means controlled by said relay for maintaining the desired ratio between fuel and air at all loads.

10. The combination with a furnace having automatic means for varying the amount `0f fuel and air supplied to the furnace in accordance with the demand on the furnace, of means for maintaining the desired relation between fuel and air for all loads comprising, an electric circuit having means therein which effects -a fiow of current which is a measure of the air flow, an electric circuit having means therein which effects a flow of current which is a measure of the steam flow, a balanced relay in said circuits, an adjustable resistance in at least one of said circuits for varying the relative ratio between fuel and air, and means controlled by said relay for maintaining the desired ratio between fuel and air at all loads.

11. lThe combination with a furnace, of a balanced relay having two opposed windings, means for effecting a flow 0f current in one of said windings which varies with the flow of steam from the furnace, means for effecting a flow of current in the other of said windings which varies with and serves as an indication of the rate at which air is supplied to the furnace, and means controlled by said relay for maintaining the desired ratio between steam low and air flow.

l2. In a furnace control system, the combination of means for supplying fuel to the furnace, means for supplying air to the furnace, means responsive to the load on the furnace which upon increase in such load operates automatically to increase only the supply of air to the furnace, means responsive to the load on the furnace which u on decrease in such load operates automatically to decrease only the supply of fuel to the furnace, and supplemental means which operates to adjust the fuel and air supply relatively to each other.

13. In a furnace control system, the combination of means for supplying fuel to the furnace, means for supplying air to the. furnace, means responsive to the load on the furnace and which upon increase insuch load operates automatically to increase only the supply of air to the furnace. and a balanced relay which operates to adjust the fuel to correspond to the changed air supply.

14. Means for maintaining a desired ratio between the amount of fuel and the amount of air supplied to a furnace, said means comprising an electric circuit having means therein which effects a flow of current which is a measure of the air flow, an electric circuit having means therein which effects a flow of current which is a measure of the steam flow, and means responsive to changes in the relative values of said currents for effecting adjustment of the fuel and air relatively to each other.

15. The combination with a furnace having means for increasing the amount of air supplied to the furnace upon increase in load and for decreasing the amount of fuel supplied to the furnace upon decrease in load, of means comprising an electric circuit having means therein which effects a flow of current which is a measure of the air fiow, an electric circuit having means therein which effects a flow of current which is a measure of the steam flow, and means responsive to changes in the relative values of said currents for effecting adjustment of the fuel and air relatively to each other.

1G. The combination with a plurality of furnaces each having fuel-supplying means and air-supplying means, of means responsive to the total furnace lo`ad for effecting adjustment of said fueland air-supplying means. and means for maintaining a desired ratio between the amount of fuel and air supplied to each furnace, said last named means comprising an electric circuit having means therein which effects a flow of current which is a measure of the air flow, an electric circuit having means therein which effects a fiow of current which is a measure of the steam flow, and means responsive to changes in the relative values of said currents for effecting adjustment of the fuel and air relativelv to each other.

1T: Means for maintaining a desired ratio between the amount of fuel and the amount of air supplied to a furnace, said means comprising an electric circuit having means therein which effects a flow of current which is a measure of the air flow, an electric circuit having. means therein which effects a How of current which is a measure of the steam flow. a balanced relay in said circuits, and means controlled by said relay for effecting adjustments of the fuel and air relatively to each other. I

18. In a furnace control system, the combination of' means for supplying fuel to the furnace, means for supplying air to the furnace, means which produces a flow of current which is a measure of the air supplied to the furnace, means which produces a flow of current which is a measure of another operating condition of the furnace, 'a balanced relay connected to said two last referred to means, and means responsive to ,changes in demand `on the furnace for effecting adjustment of the fuel and air in accordance with the load, said fuel and air being adjusted relatively to each other through the intermediary of said balanced relay.

19. In a furnace control system, the combination of means for supplying fuel to the furnace, means for supplying air to the furnace, means which produces a flow of current which is a measure of the air supplied to the furnace, means which produces a flow of current which is a measure of another operating condition of the furnace, a balanced relay connected to said two last-named means, and means responsive to changes in demand on the furnace for increasing the amount of air supplied to the furnace upon increase in load and for decreasing the amount of fuel supplied to the furnace upon decrease in load, said fuel and air being adjusted relatively to each other through the intermediary of said balanced relay.

20. In a furnace control system for a plurality of furnaces, the combination of means for supplying fuel to each furnace, means for supplying air to each furnace, means associated with `each furnace for effecting a flow of electric current proportional to the flow of air to the furnace, means associated with each furnace for effecting a flow of electric current which is proportional to another operating condition of the furnace, a balanced relay connected to said two last-named means, and means responsive to changes in demand onl the furnaces for effecting the adjustment of the fuel and air in accordance with the load, the fuel and air for each furnace being adjusted relatively to each other through the intermediarv if said balanced relays.

21. In a furnace control system for a pluralty of furnaces, the combination of means for supplying fuel to each furnace, means for supplying air to each furnace, means associated with each furnace for effecting a flow of electric current proportional to the air supplied to such furnace, means associated with each furnace for effecting a flow of electric current proportional to another operating condition of such furnace, a balanced relay connected to said two last-named means, and means responsive to changes in demand on the furnaces for increasing the amount of air supplied to each furnace upon increase in load and for decreasing the amount of fuel supplied to each furnace upon decrease in load, the fuel and air for each furnace being adjusted relatively to each other through the intermediary of said balanced relays.

22. In a furnace' control system for a plurality of furnaces, the combination of means for supplying fuel to each furnace, means for supplying air to each furnace, means associated with each furnace for effecting a flow of electric current proportional to the air supplied to such furnace, means associated with each furnace for effecting a How of electric current proportional to another operating condition of the furnace, a balanced relay connected to said two last-named means, a measuring device which produces a flow of electric current which changes upon change in the demand on the furnace, a master relay connected to said measuring device, and means controlled by said master relay for effecting regulation of the fuel and air to all the furnaces, the fuel and air of each furnace being adjusted relatively to each other by said balanced relays.

23. The combination with a furnace having means for supplying fuel and means for supplying air thereto, of a control system comprising means which produces a flow of electric current which is a measure of the air supplied to the'furnace, means for producing a fiow of electric current which is a measure of another operating condition of the furnace,-

`a balanced relay connected to sai-d two lastnamed means, means controlled by said balanced relay for adjusting the fuel and air relatively to each other, and adjustable means in the relay connections for changing the relative ratio of fuel and air.

24. The combination with -a furnace, of a balanced relay having two opposed windings, means for effecting a flow of current in one of said windings which varies with the amount of air supplied to the furnace, means for effecting a flow of current in the other of said windings which varies with another operating condition of' the furnace` and means controlled by said relay for maintaining the desired ratio between fuel and air.

25. The combination with a furnace having means for increasing the amount of air supplied to the furnace upon increase in load and for decreasing the amount of fuel supplied to the furnace upon decrease in load, of means comprising an electric circuit having means therein which effects a flow of current which is a measure of the air flow, an electric circuit having means therein which effects a. fiow of current which is a measure of another operative condition of the furnace, and means responsive to changes in the relative values of said currents for effecting adjustment of the fuel and air relatively to each other.

In witness whereof, l have hereunto set my hand this 19th day of January, 1926.

ARTHUR R. SMITH. 

